It is considered highly desirable by the obstetrician to monitor the viability of the fetus in-utero during the early and late phases of labor. At present, the most reliable methods of monitoring involve placement of a needle probe on the presenting part of the fetus; however, this procedure is technically difficult by direct manipulation during the early phases of labor because the cervix has not yet begun to dilate, necessitating the introduction of some type of narrow tubular applicator device into the birth canal such that the probe can be placed by remote external manipulation.
Various devices are known which may be used to facilitate the implantation of biological needle probes on an organ or fetus within a living body. A German Pat. No. 2,004,422 to Kresse in 1970 describes a long spiral electrode inserted through a hollow needle. The spiral is attached at its proximal end to a drive plunger. U.S. Pat. No. 4,000,745 to Goldberg describes a spiral electrode wound around a central needle used as an inserting tool for rapid placement of a pacemaker electrode in the human heart and U.S. Pat. No. 3,835,864 to Rasor describes a remote controlled device for screwing a retaining coil into the heart. The coil/carrier is rotated by a flexible drive tube inside a guide tube. A central retaining rod is coupled to the coil holder through a threaded end which operates to release the coil holder from the retaining rod after the coil is attached to the heart, using the drive tube to rotate the coil holder.
More to the point, numerous applicators have been deviced which are used specifically for the purpose of placing electrocardiogram electrodes on the human fetus while in the womb by traversing the birth canal after the onset of labor. Generally, these electodes are embedded in an insulating carrier assembly through which electrical wires or tubes are attached and, in the case where multiple electrodes are used, fixed spatial relationships between electrodes are maintained by virtue of such carrier mounting.
In U.S. Pat. Nos. 3,750,650 and 3,804,080 Ruttgers first proposed the combination of dual spiral "catcher" electrode(s) and a "counter" or reference electrode, disposed on a common insulating carrier, with two emanating electrical conductors which lead to external electrocardiogram monitoring equipment. An applicator device basically composed of two long concentric tubes, surrounding the emanating electrical conductors was disclosed which allowed for remote (i.e., external) manipulation and placement of the electrode/carrier assembly via a removeable intermating with the guide tube assembly. Remote twisting of the central tube, along with application of forward force was used to secure the electrodes.
The "Bipolar Electrode Structure For Monitoring Fetal Heartbeat and the Like" of Hon, et al., (U.S. Pat. No. Re 28,990) includes an applicator consisting of a "form-sustaining" guide tube through which a more flexible drive tube is advanced. The distal end of the drive tube has a "cooperating means" to engage the rear portion of the electrode disposed in the guide tube. Where a means for connecting an electrode to a monitor apparatus is needed, the signal leads are threaded through the common center of the drive and guide tubes from the electrode carrier assembly and ultimately exit at the proximal end of the drive tube. In a similar fashion to Ruttgers, a forward-twisting force is applied to the drive tube to effect placement of the electrode/carrier assembly, whereupon the drive tube and then the guide tube are pulled back and removed. The leads, having stripped wire on their proximal ends, are allowed to slip through the center of the guide and drive tubes, while remaining attached to the electrode/carrier assembly which in turn is secured to the fetus. The leads are connected to the monitor apparatus, but only after completion of the insertion procedure and removal of the guide and drive tubes.
Neward (U.S. Pat. No. 3,910,271) discloses a "Method of Making a Bipolar Electrode Structure" yielding an application device similar to that of HON, but incorporating flexible guide and drive tubes and a moulded wire clamping device at the proximal end of the drive tube for the purpose of holding the drive tube and electrode/carrier assembly intimately in contact during the initial phase of insertion.
Dali (U.S. Pat. No. 3,956,497) similarly improved upon the invention of Hon by adding molded wire clamp at the proximal end of the drive tube.
Showell, et al., (U.S. Pat. No. 4,151,835) discloses "FETAL SCALP ELECTRODES" incorporating an integral applicator consisting of an arcuate needle and flexible drive shaft which secures the distal end of the device to the fetal epidermis and acts as a fetal electrocardiogram electrode. The proximal end of the drive shaft is external and incorporates a knob for engaging the needle and a centrally located pair of wires for interconnection to monitoring equipment.
Murphy (U.S. Pats. Nos. 4,149,528, and 4,180,080) discloses an "Electrode Assembly for Sensing Heart Activity" wherein the twisted, interconnecting electrode wires are rotated from their proximal ends to effect rotation of the electrode/carrier assembly. The wires travel through the center of a flexible guide tube. A safety stop and wire disengaging means are additional features of this invention.
Ferrar, et al, disclose "push-in" fetal electrode designs of a tuberous shape and applicators therefore in U.S. Pat. No. 4,244,375.
Helfer (U.S. Pat. No. 4,437,467) and Hon (U.S. Pat. No. 4,321,931) have disclosed revised carrier structures and mating applicators therefore which incorporate linear-to-rotary motion convertors with the objective of allowing the physician to place the spiral electrode by pushing on a plunger located at the proximal end of the applicator rather than pushing and rotating a drive tube.
In addition to the aforementioned inventions for monitoring of fetal electrocardiograms, several pH sensing electrodes have been conceived which incorporate spiral retaining coils for direct implantation into the fetus while in the womb. The "Electrode Cell Assembly" of Moller, et al (U.S. Pat. No. 3,973,555) does not describe an applicator means and presumably was inserted under direct manipulation. Ferrar, et al (U.S. Pat. No. 4,281,659) discloses an applying and securing means for fetal pH probe. First, large diameter guide and drive tubes are used to place a stable platform on the fetal epidermis secured by two spiral "catcher" needles. A lance mounted on a yet smaller tube is then advanced through the center of the drive tube to pierce the fetal epidermis. Finally the third tube is withdrawn and the cylindrical shaped pH probe is advanced through the center of the drive tube by attaching it to the end of a C-shaped channel. A total of five separate applicator parts are employed, not including the probe itself.
Finally, Bernard (U.S. Pat. No. 4,294,258) describes a "slanted-needle" pH probe with an integral applicator. The applicator employs two arcuate claws and an interconnecting cable which allows remote deployment of the claws. In an alternative embodiment, the pH probe is described as incorporated in two spiral-shaped hollow-needle electrodes on a common carrier but the applicator system is not described.
Each of the foregoing prior-art techniques of fetal probe application has its own drawback and limitation. Having not the aid of a guide tube to traverse the cervix, the devices of Showell and Bernard are difficult to apply during the early phases of labor. In addition, Ferrar's tuberous electrodes and applicators, as well as the devices of Kresse, Goldberg, and Moller, pose a risk of injury to the mother and/or fetus during the insertion procedure because needle structures that may penetrate tissue are exposed during transit of the birth canal.
And finally, the devices of Ruttgers, Rasor, Hon, Neward, Murphy, Helfer, and Ferrar (pH electrode applicator), although enjoying the relative safety and improved placement characteristic of employing a guide tube as part of the applicator, all suffer from a common drawback as related to the application of bioprobes employing spiral retaining coils. This drawback is that the monitor interconnecting cable, which conveys the probe signal from its location in situ to the external monitoring equipment, and which most commonly takes the form of wire(s), cable(s), or tube(s), must traverse laterally the hollow center of the guide and drive tube apparatus. This, in turn, means that the guide and drive tubes (which are necessarily small in diameter in order to transit the closed cervix) and which are withdrawn after placement of the probe/carrier assembly, and the proximal end(s) of the aforementioned wires, tubes, or cables--that connect to the monitor apparatus--must be necessarily of a diameter smaller than the guide and drive tubes.
This problem has been resolved in the prior art by use of stripped and tinned ends on the wires which, after probe insertion and applicator removal, are connected to a set of compression-type binding posts as a means of achieving a reliable signal connection to the monitor apparatus. While this type of connection achieves a reasonably inexpensive way of circumventing the diameter restriction placed on the proximal end of the monitor interconnecting cable, it places severe restriction on the types and complexity of signals which may be carried by the monitor interconnecting cable. For instance, where it is desired to connect more than 2 or 3 separate wires to the monitor apparatus, it is impractical to use bare-wire connections as described above because of the possibility of connecting the wires to the wrong posts.
In order to reduce connection time and confusion of multiple wires, it is desirable to use a cable connector, which for reasons of reliability and cost, typically has a maximum diameter which is larger than can be passed over by the guide and drive tubes.
Further, the bare-wire binding post type of interconnection, although suitable for electrical signals such as the 2-lead fetal electrocardiogram, is not useable where at least one of the signals being conveyed by the monitor interconnecting cable is transmitted light via a fiber optic cable, such as the spiral probes disclosed in FIG. 7 of copending U.S. patent application Ser. No. 685,154, and/or where the monitor interconnecting cable employs tubes for carrying fluids to or from the fetus, as disclosed by Ruttgers. For these latter types of spiral probes, operation is practical only with resort to cable-mounted fiber optic and/or fluid fittings (connectors) located at the proximal end of the monitor interconnecting cable.
A further disadvantage of the prior art of Ruttgers and others is that, as a result of the requirement that the guide and drive tube must be withdrawn over the proximal extremity of the monitor interconnecting cable, it is necessary to break the monitor interconnection while the guide and drive tubes are being withdrawn. This results in a temporary loss of monitoring information about the fetus, and in the case of certain probes which must be precalibrated prior to insertin (e.g., ion or gas sensing probes), breaking of monitor interconnections after insertion may result in a loss of probe calibration. From the foregoing it can be appreciated that it is highly desirable to conceive of a probe applicator device which allows the use of relatively large diameter cable connectors of various signal-carrying or fluid carrying types at the proximal end of the monitor interconnecting cable.